Journal Article

Measurements of global and local spin polarization of Λ and Λ in Au+Au collisions from the RHIC Beam Energy Scan

Hu, Qiang

2025

Overview

We report the measurements of Λ hyperons’ global and local spin polarization from second phase of the RHIC Beam Energy Scan (BES-II) in Au+Au collisions at Λ and Λ¯ = 7.7−27 GeV. Global polarization measurements of Λ and Λ show no significant differences, offering insights into the late-stage evolution of the magnetic field. The new measurements of the local polarization of Λ perpendicular to the reaction plane (< P 2, y >) shows a monotonic increase with decreasing collision energy, while the component along the beam direction (< P 2, y >) for both Λ and Λ is small in magnitude with no strong energy dependence. The net local polarization observable, Λ and Λ¯ and 〈 P 2,y net > = 〈 P 2,y (Λ)〉 - 〈 P 2,y (Λ¯)〉 and 〈P 2,z net 〉 = 〈P 2,z (Λ)〉 - 〈P 2,z (Λ¯)〉 designed to probe baryonic spin Hall effect, is consistent with zero with large uncertainty.

• Publisher: EDP Sciences
• Subject: Collisions / Hall effect / Hyperons / Polarization (spin alignment) / Relativistic Heavy Ion Collider